iOS 6 audio framework bug may be to blame for data overages

Public Radio Exchange claims it's fixed in iOS 6.0.1, but users aren't so sure.

PRX Labs, an extension of the Public Radio Exchange, has pinpointed what it believes is the cause of iPhone data overages since the launch of iOS 6. In a blog post, PRX says Apple's Audio Playback frameworks are causing iOS devices to download audio files multiple times while a user is streaming, "using significant amounts of data" when the user is on an LTE or 3G network. And while PRX believes the bug was squashed in iOS 6.0.1, some iPhone users aren't quite so sure.

The team at PRX said they saw a "pretty intense spike in traffic" on two of its popular podcasts last month—followed by concerns brought up by the team from This American Life—which sparked an investigation into Apple's new Podcasts app and iOS 6. PRX offers more details about how it pinpointed the problem in its blog post, but the general gist is that they watched their own traffic logs along with user agent strings, discovering that those running iOS 6 appeared to be downloading audio files multiple times compared to folks on iOS 5. This bug was present in both the Podcasts app as well as PRX's own show-specific apps, leading the team to cite the system-wide AV Foundation framework as the cause of the problem.

Enlarge/ PRX Labs saw abnormal download spikes following the release of iOS 6 and began to investigate.

"The player appears to get into a state where it makes multiple requests per second and closes them rapidly. Because the ranges of these requests seem to overlap and the requests themselves each carry some overhead, this causes a single download of an MP3 to use significantly more bandwidth than in iOS 5. In one case, the playback of a single 30MB episode caused the transfer of over 100MB of data," reads the blog post.

"The strangest bit of behavior happens when the ranges on these requests reach the end of the file. We were able to consistently see that when the file has completed downloading, it begins downloading again from the beginning of the file and continues for as long as one is streaming the file. This means that, for as long as one is listening to audio being streamed with iOS 6, it is using significant amounts of data."

The report comes just over a month after Verizon said it wouldn't charge iPhone 5 users for erroneous data usage that seemed to be triggered by a problem staying connected to Wi-Fi. That bug was reportedly fixed by a carrier settings update, but it sounds as if there were multiple issues contributing to higher-than-normal data usage. If PRX's discovery is correct, the bug likely affected numerous other audio apps—and possibly video apps as well.

According to PRX, the bug isn't reproducible under iOS 5 or iOS 6.0.1. But in a recent Apple discussion thread (hat tip to The Next Web), some users who have upgraded to iOS 6.0.1 claim to still be seeing extraordinary data consumption from their iPhones. I know my own cellular data use has gone up significantly since upgrading to an iPhone 5 with iOS 6 (now iOS 6.0.1), even though my behavior patterns have stayed the same—I went from consuming about 250MB per month to 1.6GB per month with no obvious changes to how I use my phone.

Have you been seeing the same pattern? Do you think it has decreased since the release of iOS 6.0.1 at the beginning of November? Let us know.

Apple did not respond to request for comment by publication time, but we'll update if we get a response.